1. Field of the Invention
The present invention relates in general to a fiber optic displacement sensor, and in particular, it is directed to a fiber optic microbend displacement sensor employing a coiled optical fiber exposed to a parameter. A change in the parameter causes a change in the coil length and pitch which effects a light throughput to change in corresponding manner.
2. Description of the Related Art
There are displacement sensors currently available based on a wide variety of electrical sensing techniques. These include variable reluctance, eddy current and linear variable differential transformers (LVDT).
While these existing techniques are used successfully for measuring displacement, they employ electrical fields and voltages in the sensors that may be suseptible to signal degradation depending on the physical and electrical environment.
Microbend sensors in general offer the advantages of being simple, low cost, immune to electro-magnetic interference, operable over wide ranges of temperature, pressure and other environmental conditions. In addition, good performance can be obtained with relatively simple opto-electronics. Current fiber optic microbend sensor technology requires additional external structures such as corrugated plates. These additional external structures add costs in terms of material and time as well as being suitable only for certain applications.
U.S. Pat. No. 4,891,511 discloses a fiber optic microbend sensor employing braided fibers. The arrangement of the fibers provides length dependent microbending losses from the interaction of the fibers themselves.
There are currently available optical fluid level sensors based on an array of individual optical fibers with the tip of each fiber situated at a fluid level interval for measurement. These types of sensors utilize reflection and/or refraction as taught in U.S. Pat. Nos. 4,764,671; 4,942,306; 4,633,711; 4,038,650; 4,870,292; 4,745,293; and 4,994,682.
There is a need for a fiber optic microbend sensor which is simple, accurate, and readily attachable to structures with several applications. It should not require precision in the attachment and be economical.